What must I consider in placing the fiducial marks?

Perfect cutting of printed material

Many applications require precise cutting to existing fiducial marks or other material reference points. eurolaser offers an intelligent solution for this purpose, consisting of a CCD camera and evaluation software: LaserScout POSITIONplus.

Scanning of fiducial marks

The CCD camera is installed directly on the processing head and searches for the workpiece using defined fiducial marks at the start of the processing procedure. In this manner, printed, woven or embroidered fiducial marks as well as edges or other high-contrast contours can be visually scanned. The actual position and dimensions of the workpiece are thus recognised exactly and taken into account for further processing.

The eurolaser LaserScout POSITION software is generally able to recognise a range of different fiducial marks. In order to achieve the best possible level of recognition and reliability, we have put together a few hints. These are not, of course, binding requirements, but help ensure a smooth processing experience and increase productivity.

Please consider the following features:

Form

The form or appearance of a fiducial mark is its most marked characteristic. LaserScout POSITION is able to recognise a range of forms. Circles are the most suitable for camera recognition, since the midpoint of the circle is equidistant from all sides. This is the decisive advantage. A cross, for example (+), can easily be transformed into an X and is no longer recognised if the printing is rotated.

Image 1

Image 2

Contrast

In creating the marks ensure that there is sufficient contrast between the mark and the background. Image 1 shows a very good contrast. A black mark is placed on a white background. No background or printing which would break up the circle shows through this. Image 2 has a poor choice of background. It does not ensure easy legibility, and can result in difficulties with the recognition process. Ensure that there is adequate lighting in the surrounding work area.

Size

The camera which sends the image signal to the software is located directly on the tool head. It thus always covers a specific area of the table surface which comprises approximately 30 x 30 mm. Fiducial marks should have a diameter of approximately 6 mm so that they can be easily recognised within this area.

Image 3

Image 4

Number

For every motif that is to be cut out a minimum of three fiducial marks, placed at the corners of the motif, are required. In general, the following also applies: the more fiducial marks available, the more accurate the result. In image 3 individual fiducial marks for each motif can be seen. There are more fiducial marks along the length of the motif, and the result is consequently more precise. In image 4 only a set of fiducial marks in the corners of the whole array has been provided. If only the outer marks are available they should only be used for placement. In order to compensate for print displacement, we recommend using several fiducial marks.

Uniformity

The fiducial marks should be uniform in shape and size for optimal results. Different marks have different offset values, and reading them in can take longer than when all marks are uniform, increasing production times.

If you take account of these five characteristics of fiducial marks you will optimise your work flow and exploit the full potential for precise cutting of printed motifs.